Method of overmolding a substrate and product made by that process

ABSTRACT

A method of overmolding a substrate having a first side and a second side and a product made by that process. A plurality of support feet are placed on the first side of the substrate. The substrate is placed in an injection mold. The mold is filled with a molding material with the molding material enveloping both the first side and the second side of the substrate. The substrate is removed having been overmolded from the injection mold.

FIELD OF THE INVENTION

The present invention relates generally to a method of overmolding asubstrate and, more particularly, to a method of overmolding a substrateon both sides of the substrate, and a product made by that method.

BACKGROUND OF THE INVENTION

Implantable medical devices for producing a therapeutic result in apatient are well known. Examples of such implantable medical devicesinclude implantable drug infusion pumps, implantable neurostimulators,implantable cardioverters, implantable cardiac pacemakers, implantabledefibrillators and cochlear implants. Some of these devices, if not all,and other devices either provide an electrical output or otherwisecontain electrical circuitry to perform their intended function.

Such implantable medical devices, when implanted, are subjected to aharsh environment in contact with bodily fluids. Such bodily fluids canbe corrosive to the implantable medical device. Typically, implantablemedical devices are hermetically sealed, often in a titanium case, inorder to protect the implantable medical device from the harmful effectsof the bodily fluids with which the implantable medical device comesinto contact.

The securing of an implantable medical device against infiltration ofbody fluids which may compromise the integrity and/or reliability of theimplantable medical device can lead to very tight tolerances inconstruction and/or assembly and rigid positioning and fastening ofcomponents within the housing of the implantable medical device. Anybreach of an otherwise hermetically sealed case could lead toinfiltration of body fluids into the implantable medical device andpossibly result in a premature failure of the device.

This problem is exacerbated in newer electrically stimulating devicesutilizing recharging technology where the implanted secondary coil andelectrical contacts are located outside of the titanium case. Theproblem is further exacerbated by an increase in the number ofexcitation electrodes for use in patient therapy, therefore resulting inan increase in the number of electrical connections made outside of thetitanium case. With the implanted secondary coil and the greater numberof electrical contacts located outside of the titanium case, the greaterthe problem of making a secure, reliable connection without riskingcompromise of the implantable medical device and possible subsequentpremature failure. Failure of an implanted medical device could lead notonly to necessary surgery to explant the device but could jeopardize thepatient's well being by making the therapeutic advantages of the medicaldevice unavailable to the patient until explantation and re-implantationcould occur.

Components used in implantable medical devices are often overmolded witha protective overmold as a step in protecting the components against theinfiltration of body fluids. While such overmolding is often effectiveat protecting such components, care must be taken not to damage thecomponent, or substrate, being overmolded as a result of the overmoldingprocess.

BRIEF SUMMARY OF THE INVENTION

Generally planar substrates are sometimes relatively fragile to warpingor bending. When overmolding is not done carefully, stresses createdduring overmolding can lead to warping or bending of the substratepossibly rendering it useless for its intended or, worse, possiblyimpairing its reliability. Reliability, as mentioned above, is criticalin an implantable medical device.

Further, molding material tends to shrink or crack as it cools followingthe molding process. Such shrinkage can lead to gaps or cracks that canallow body fluids to infiltrate the component possibly compromising itsintegrity.

Thus, there is needed a reliable and effective overmolded material and amethod of overmolding such material that reduces or eliminates theseproblems.

In one embodiment, the present invention provides a method ofovermolding a substrate having a first side and a second side. Aplurality of support feet are placed on the first side of the substrate.The substrate is placed in an injection mold. The mold is filled with amolding material with the molding material enveloping both the firstside and the second side of the substrate. The substrate is removedhaving been overmolded from the injection mold.

In another embodiment, the present invention provides an overmoldedsubstrate having a first side and a second side. A generally planarsubstrate has a plurality of support feet on the first side of thesubstrate. A molding material is molded around the substrate envelopingthe substrate of both the first side and the second side of thesubstrate.

In another embodiment, the present invention provides an overmoldedsubstrate having a first side and a second side. A generally planarmagnetic substrate has a coil positioned on the second side of themagnetic substrate. The magnetic substrate has a plurality of supportfeet on the first side of the magnetic substrate. A molding materialmolded around the substrate enveloping the magnetic substrate on boththe first side and the second side of the magnetic substrate.

In a preferred embodiment, the molding material is substantially evenlydistributed on the first side and the second side during the fillingstep.

In a preferred embodiment, a plurality of support feet are placed on thefirst side of the substrate.

In a preferred embodiment, the substrate has a central hub opening.

In a preferred embodiment, the injection mold has injection openings onone side of the injection mold and wherein the molding material isinjected into the mold through the injection openings.

In a preferred embodiment, the substrate is placed in the injection moldwith the first side of the substrate facing the one side of theinjection mold.

In a preferred embodiment, the molding material is distributed to thesecond side of the substrate through the central hub opening.

In a preferred embodiment, the feet have a circular cross-section.

In a preferred embodiment, the molding material forms around each of theplurality of feet.

In a preferred embodiment, the central hub opening has a circular postaround which the molding material is allowed to form.

In a preferred embodiment, the support feet are molded in a firstmolding step and the molding material is molded around the substrate ina second molding step.

In a preferred embodiment, the substrate is overmolded only from thefirst side of the substrate.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates an implantable medical device implanted in a patient;

FIG. 2 is a block diagram of an implantable medical device illustratingenergy transfer from an external charging device;

FIG. 3 is a top view of a base laminate used in an internal antenna inan implantable medical device;

FIG. 4 is a side cross-sectional view the base laminate of FIG. 3;

FIG. 5 is a top view of coil ready coreless laminate formed from thebase laminate of FIGS. 3 and 4;

FIG. 6 is an perspective view of the laminate of FIG. 5 having receiveda secondary charging coil;

FIG. 7 is an illustration of a pressure lamination process securingcover sheets to the laminated substrate;

FIG. 8 illustrates the attachment of support feet in a first step in anovermolding process;

FIGS. 9A, 9B, 9C, 9D and 9E illustrate the injection molding of a secondstep in an overmolding process;

FIG. 10 is an exploded view of an internal antenna showing both theovermolded laminated substrate and a cover;

FIG. 11 is a perspective view of an internal antenna for use with animplantable medical device;

FIG. 12 illustrates an interior view of a housing of an implantablemedical device showing the positioning of a power source;

FIG. 13 is a perspective view of a battery support for an implantablemedical device;

FIG. 14 is a cross-sectional view of an implantable medical deviceshowing the placement and support of a battery;

FIG. 15 is a perspective view an internal antenna about to be mated witha housing of implantable medical device;

FIG. 16 is a detailed view of a portion of FIG. 15 illustrating anengagement tab;

FIG. 17 is another detailed view of an engagement tab for an internalantenna;

FIG. 18 is a top view of a portion of a housing for implantable medicaldevice illustrating bottom rail engagement and fill hole;

FIG. 19 is a detailed view of internal antenna mounted to housingillustrating sealing implantable medical device using an adhesiveneedle;

FIG. 20 is a cross-sectional view of a portion of internal antenna andhousing illustrating a flow channel for an adhesive sealant;

FIG. 21 is an exploded view of a connector block for use with animplantable medical device;

FIG. 22 is a cross-sectional view of the connector block of FIG. 21;

FIG. 23 is a partial cross-section view of the connector block of FIG.21 illustrating a chimney; and

FIG. 24 is an exploded view illustrating the assembly of internalantenna, housing and connector block of implantable medical device.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 shows implantable medical device 10 for example, a drug pump,implanted in patient 12. The implantable medical device 10 is typicallyimplanted by a surgeon in a sterile surgical procedure performed underlocal, regional, or general anesthesia. Before implanting the medicaldevice 10, a catheter 14 is typically implanted with the distal endposition at a desired location, or therapeutic delivery site 16, in thebody of patient 12 and the proximal end tunneled under the skin to thelocation where the medical device 10 is to be implanted. Implantablemedical device 10 is generally implanted subcutaneously at depths,depending upon application and device 10, of from 1 centimeter (0.4inches) to 2.5 centimeters (1 inch) where there is sufficient tissue tosupport the implanted system. Once medical device 10 is implanted intothe patient 12, the incision can be sutured closed and medical device 10can begin operation.

Implantable medical device 10 operates to infuse a therapeutic substanceinto patient 12. Implantable medical device 10 can be used for a widevariety of therapies such as pain, spasticity, cancer, and many othermedical conditions.

The therapeutic substance contained in implantable medical device 10 isa substance intended to have a therapeutic effect such as pharmaceuticalcompositions, genetic materials, biologics, and other substances.Pharmaceutical compositions are chemical formulations intended to have atherapeutic effect such as intrathecal antispasmodics, pain medications,chemotherapeutic agents, and the like. Pharmaceutical compositions areoften configured to function in an implanted environment withcharacteristics such as stability at body temperature to retaintherapeutic qualities, concentration to reduce the frequency ofreplenishment, and the like. Genetic materials are substances intendedto have a direct or indirect genetic therapeutic effect such as geneticvectors, genetic regulator elements, genetic structural elements, DNA,and the like. Biologics are substances that are living matter or derivedfrom living matter intended to have a therapeutic effect such as stemcells, platelets, hormones, biologically produced chemicals, and thelike. Other substances may or may not be intended to have a therapeuticeffect and are not easily classified such as saline solution,fluoroscopy agents, disease diagnostic agents and the like. Unlessotherwise noted in the following paragraphs, a drug is synonymous withany therapeutic, diagnostic, or other substance that is delivered by theimplantable infusion device.

Implantable medical device 10 can be any of a number of medical devicessuch as an implantable pulse generator, implantable therapeuticsubstance delivery device, implantable drug pump, cardiac pacemaker,cardioverter or defibrillator, as examples.

Electrical power for implantable medical device 10 can be contained inimplantable medical device itself. Power source for implantable medicaldevice 10 can be any commonly known and readily available sources ofpower such as a chemical battery, electrical storage device, e.g.,capacitor, a mechanical storage device, e.g., spring, or can betranscutaneously supplied in real time, or some combination.

In order to achieve a transcutaneous transfer of energy, either tocharge or recharge an implanted battery or to supply real time powersupply, or some combination, an inductive charging technique using anexternal primary coil and an internal secondary coil can be utilized.

FIG. 2 illustrates an embodiment of implantable medical device 10situated under cutaneous boundary 18. Charging regulation module 20controls the charging of rechargeable power source 22. Power source 22powers electronics module 24 which, in turn, controls therapy module 26.Again, charging regulation and therapy control is conventional.Implantable medical device 10 also has internal telemetry coil 28configured in conventional manner to communicate through externaltelemetry coil 30 to an external programming device (not shown),charging unit 32 or other device in a conventional manner in order toboth program and control implantable medical device and to externallyobtain information from implantable medical device 10 once implantablemedical device has been implanted. Internal telemetry coil 28,rectangular in shape with dimensions of 1.85 inches (4.7 centimeters) by1.89 inches (4.8 centimeters) constructed from 150 turns of 43 AWG wire,is sized to be larger than the diameter of secondary charging coil 34.Secondary coil 34 is constructed with 182 turns of 30 AWG wire with aninside diameter of 0.72 inches (1.83 centimeters) and an outsidediameter of 1.43 inches (3.63 centimeters) with a height of 0.075 inches(0.19 centimeters). Magnetic shield 36 is positioned between secondarycharging coil 34 and housing 38 and sized to cover the footprint ofsecondary charging coil 34.

Internal telemetry coil 28, having a larger diameter than secondary coil34, is not completely covered by magnetic shield 36 allowing implantablemedical device 10 to communicate with the external programming devicewith internal telemetry coil 28 in spite of the presence of magneticshield 36.

Rechargeable power source 24 can be charged while implantable medicaldevice 10 is in place in a patient through the use of external chargingdevice 40. In a preferred embodiment, external charging device 40consists of charging unit 32 and external antenna 42. Charging unit 32contains the electronics necessary to drive primary coil 44 with anoscillating current in order to induce current in secondary coil 34 whenprimary coil 44 is placed in the proximity of secondary coil 34.Charging unit 32 is operatively coupled to primary coil by cable 46. Inan alternative embodiment, charging unit 32 and external antenna 42 maybe combined into a single unit. Antenna 42 may also optionally containexternal telemetry coil 30 which may be operatively coupled to chargingunit 32 if it is desired to communicate to or from implantable medicaldevice 10 with external charging device 40. Alternatively, externalantenna 42 may optionally contain external telemetry coil 30 which canbe operatively coupled to an external programming device, eitherindividually or together with external charging unit 32.

Repositionable magnetic core 48 can help to focus electromagnetic energyfrom primary coil 30 to more closely be aligned with secondary coil 34.Energy absorptive material 50 can help to absorb heat build-up inexternal antenna 42 which will also help allow for a lower temperaturein implantable medical device 10 and/or help lower recharge times.Thermally conductive material 52 is positioned covering at least aportion of the surface of external antenna 42 which contacts cutaneousboundary 18 of patient 12. Thermally conductive material 52 positionedon the surface of external charging device 40 in order to distribute anyheat which may be generated by external charging device 40.

Secondary coil 34 is located in internal antenna 54 that is separablefrom housing 38. Magnetic shield 56 is positioned between secondary coil34 and housing 38 and inside the diameter of internal telemetry coil 28to help isolate the remainder of implantable medical device 10 fromelectromagnetic energy from external charging device 40.

In FIG. 3 and FIG. 4, construction of internal antenna 54 begins withbase laminate 58. Base laminate 58 is constructed of a plurality oflayers, preferably three layers, of Metglas™ material 59 securedtogether by a suitable adhesive, such as Pyralux® acrylic adhesive. Eachlayer of Metglas™ material 59 is approximately 0.001 inch (0.0254millimeters) thick. Eight eddy current grooves 60 are radially etched bylaser into one side of the layers of Metglas™ material 59 atapproximately equal radial spacings. An insulative layer of polyimide isadhesively secured to each side of Metglas™ laminate resulting in a baselaminate 58 approximately 0.15 inches (3.8 millimeters) thick. Baselaminate 58 is approximately 1.54 inches (39 millimeters) square withtwo rounded comers to facilitate subsequent assembly.

Lead wires 62 are placed (FIG. 5) onto base laminate 58 with endspositioned at locations adapted to connect with wires from a coil toadded to base laminate 58. Lead wires 62 are placed inboard and,generally, away from cutouts for hub 64 and feet 66. Preferably, leadwires 62 are flat 0.004 inch (0.10 millimeters) and round 0.015 inch(0.38 millimeters) in locations 70 and 72 exiting base laminate 58.Preferably, lead wires 62 are made from niobium ribbon wire. Oncepositioned, lead wires 62 are secured in place by adhesively securinganother layer 63 of polyimide to the side of base laminate 58 onto whichlead wires 62 have been positioned. The resulting structure forms a coilready coreless laminate 68 ready to receive a coil of wire that formssecondary coil 34. Pre-placing lead wires 62 onto base laminate 58reduces stress from normal movement of lead wires 62 and aids in furtherassembly.

Prior to being placed onto the surface of coil ready coreless laminate68, secondary coil 34 is preferably coated in a siloxane coatingprocess. Secondary coil 34 is placed in a vacuum chamber that is thenevacuated to 0.10 torr vacuum and held for ten (10) minutes. 10 sccm ofHexamethyldisiloxane, 30 sccm of Nitrous oxide and 1 sccm of Argon arepumped into the chamber. Approximately 150 watts of power to ignite theplasma for thirty (30) seconds.

In FIG. 6, secondary coil 34 is then placed onto the surface of coilready coreless laminate 68 and electrically connected to lead wires 62at locations 70 and 72 by welding or, preferably, opposed welding.Cross-over copper wire 74 from secondary coil 34 makes electricalconnection at location 72. The resulting substrate 80 is then sandwichedbetween a cover sheet 76 of polyimide secured with a thermoset adhesiveas illustrated in FIG. 7. Substrate 80 is placed into a press betweenpolyimide cover sheets 76 which, of course, can be added either beforeor after substrate 80 is placed into the press. A thermoset adhesive,preferably Pyralux® acrylic adhesive, is located between substrate 80and cover sheets 76. A liquid thermoset polymer, such as liquid siliconerubber, is added to the press outside of cover sheets 76. Heat,preferably approximately 340 degrees Fahrenheit, and pressure,preferably approximately 1,200 pounds per square inch (8,274 pascals),are applied in the press forcing liquid thermoset polymer again coversheets 76 which are, in turn, pressed against substrate 80. The use of aliquid material in the press allows the press to apply force evenlyagainst the irregular upper surface of substrate 80. The thermosetpolymer is allowed to cure under heat and pressure for approximatelyfive (5) minutes forming an at least partially cured silicone rubbersheet on either side of substrate 80 and allowed to cool forapproximately twenty (20) minutes. The assembly can then be removed fromthe mold and the silicone rubber sheets removed (peeled) away anddiscarded leaving the laminated substrate 80.

This process can increase the efficiency of laminating a plurality ofarticles. The press is only used during while the liquid thermosetpolymer is being pressed to substrate 80. Once the liquid thermosetpolymer has cured, e.g., approximately five (5) minutes, the laminatedsubstrate 80 may be removed from the press. The laminated substrate 80can continue to be allowed to cool outside of the press, e.g., forapproximately twenty (20) minutes. As soon as the first laminatedsubstrate 80 is removed from the press, the press may be used again toproduce a second laminated substrate 80. Since the laminated substrate80 need only remain in the press during the initial stages (first five(5) minutes) for curing, the press may be used to produce a secondlaminated substrate 80 while the first laminated substrate 80 continuesto cool. The early re-use of the press, as compared with having to alonglaminated substrate to remain in the press for the entire cooling time,is a consider savings in equipment time and allows a greatly increasedefficiency of operation.

Laminated substrate 80 is then overmolded to seal laminated substrate inan environment better able to withstand the harmful effects of bodilyfluids after implantation. The overmolding takes place in two steps. Inthe first step shown in FIG. 8, a plurality of support feet 82 areplaced on one side, preferably the underside, of laminated substrate 80.Support feet 82 may be molded onto the underside of laminated substrate80 using conventional molding techniques. Alternatively, support feet 82may be adhesively attached, e.g., with glue, may be ultrasonicallystaked or may be otherwise mechanically attached, e.g., by threadedfastener. Support feet 82 may be equally spaced somewhat near each ofthe four corners of laminated substrate 80. In a preferred embodiment,support feet have a circular cross-section. Preferably hub 84 is alsomolded, or otherwise mechanically attached, to laminated substratesurrounding a central hole in laminated substrate.

The second part of the overmolding process is illustrated in FIGS. 9A,9B, 9C and 9D. In FIG. 9A, laminated substrate 90 with support feet 82and hub 84 is placed into an injection mold. Injection material 85,preferably polysulfone, is introduced into the mold through five (5)injection holes (86A, 86B, 86C, 86D and 86E) from one side of theinjection mold. Please note that the FIGS. 9A, 9B, 9C and 9D represent across-sectional view of the injection mold. Although a total of five (5)injection holes are utilized, only three (3) are visible in thecross-sectional view. One (1) injection hole is used for the hub(injection hole 86B). Four (4) injection holes are equally spaced asillustrated in FIG. 9E. Note that injection holes 86D and 86E are notvisible in the cross-sectional view in FIG. 9A. Injection material 85begins to flow into the underside of laminated substrate 80 throughinjection holes 86A and 86C. Injection material 85 also begins to flowthrough hub 84 and spreads out over the topside of laminated substrate80 through injection hole 86B. In FIG. 9B, injection material 85continues to flow into the injection mold through the five (5) injectionholes (86A, 86B, 86C, 86D and 86E) in a manner such that the amount ofinjection material 85 flowing over the topside of laminated substrate 80and the amount of injection material 85 flowing over the underside oflaminated substrate 80 is such that mechanical forces against laminatedsubstrate 80 are evened out from topside and underside. Generally, thisis expected to occur when injection material 85 flows at approximatelythe same rate over the topside of laminated substrate 80 as over theunderside of laminated substrate 90. That is, injection material 85 onthe topside of laminated substrate 80 is forcing against the topside oflaminated substrate 80 with about the same amount of force thatinjection material 85 is forcing against the underside of laminatedsubstrate 80. The general evening of molding forces for topside tounderside helps stabilize laminated substrate 80 during the moldingprocess and helps to eliminate warping of laminated substrate 80. InFIG. 9C, injection material 85 continues to flow evenly over the topsideand the underside of laminated substrate 80. In FIG. 9D, injectionmaterial 85 has filled the injection mold essentially filling all of thecavity of the injection mold resulting in an overmolded laminatedsubstrate 80. Injection holes 86A, 86B, 86C, 86D and 86E are chosen insize such to facilitate the even flow of injection material 85. Ifinjection material 85 does not flow evenly over both the topside and theunderside of laminated substrate 80, the resultant overmolded part canwarp following cooling.

As shown in FIGS. 9A, 9B, 9C and 9D, injection material 85 flows aroundsupport feet 82 and encircles each of circular support feet 82. Asinjection material 85 cools following the injection molding process,injection material 85 has a tendency to shrink. Typically, shrinkage ofinjection material may create a crack or a gap which may create an areainto which bodily fluids could subsequently gain entry followingimplantation. However, by encircling each of support feet 82, suchshrinkage of injection material 85 will actually cause injectionmaterial to form more tightly around support feet 82 creating an evenstronger bond and helping to ensure that bodily fluids can not gainentry following implantation. This same technique holds true for hub 84.Hub 84 has a circular cross-section and has surrounding a indentationwhich allow injection material 85 to surround hub 84 and shrink moretightly to hub 84 as injection material 85 cools creating a strongerbond and less likelihood of leaks.

Overmolded cover 90, created in FIGS. 9A, 9B, 9C and 9D, by overmoldinglaminated substrate 88 in an injection mold, is shown in FIG. 10 withpolysulfone cover 85. Cover 90 is mechanically joined with overmoldedsubstrate 88 in a conventional manner to complete the assembly ofinternal 54 (shown in FIG. 11).

FIG. 12 shows housing 38 of portion of implantable medical device 10holding power source 22, electronics module 24 and other components.Power source (preferably a battery) 22 is located in area 92 in housing38. It is desirable that battery 22 be reasonably secured within housing38 but at the same be allowed to expand and contract with use. Chemicalbatteries, such as battery 22, may have a tendency to expand as thebattery 22 is charged and subsequently contract as the battery 22 ceasesto be charged. Such expansion and contraction in a battery 22 which isvery tightly secured in housing 38 might cause battery 22 to either comeloose from its attachments and/or compromise its electrical connections.Therefore, in a preferred embodiment battery 22 is held in a mannerwhich allows battery 22 to expand, e.g., during charging, andsubsequently contract, e.g., following charging, without compromisingmechanical and/or electrical connections. Spacer 94, seen more clearlyin FIG. 13, supports battery 22 around the periphery of battery 22 whilecutout 96 in the central portion of spacer 94 allows battery 22 toexpand without compromise. In a preferred embodiment, battery 22 has arectangular shape with major and minor sides. Preferably, spacer 94supports a major side of battery 22 while allowing cutout 96 to allowexpansion of the major side of battery 22. In a preferred embodiment,spacer 94 is constructed with a layer of polyimide approximately 0.001inch (0.0254 millimeters) thick. Preferably, spacer 94 is secured in aninside surface of housing 38 with a suitable adhesive (see FIG. 14). Ascan be seen in FIG. 14, battery 22, fits inside battery cup 97 supportedby spacer 94, is allowed to expand, e.g., during charge, as illustratedby expansion dotted lines 98. During a subsequent operation of assemblyof implantable medical device 10, epoxy 100 is introduced into housing38 to help secure battery 22. Battery cup 97 and spacer 94 will help toensure that epoxy 100 does not fill the space created by spacer 94.

FIGS. 15 through 20 illustrate the mechanical connection of internalantenna 54 to housing 38 to achieve an integrated implantable medicaldevice 10 that will be able to withstand the ravages of bodily fluidsonce implanted. Housing 38 has a recharge rail 102 extending aroundthree sides that is adapted to slideably mate with a complementary rail104 on internal antenna 54. However, electrical connector wires 106inhibit rail 104 of internal antenna 54 from engaging recharge rail 102from the open end. While electrical connector wires could be bent andthen reformed to the illustrated position following installation ofinternal antenna 54 onto housing 38, this is not desirable from areliability standpoint, due to the bending and straightening of wires106, it is also inefficient. Recharge rail 102 has a drop opening 108allowing tab 110 of internal antenna 54 to drop into opening 108 andthen allow rail 104 to slidably engage recharge rail 102 which areconfigured to slidably engage over a portion of the sliding distance.This “drop and slide” engagement allows internal antenna 54 to dropavoiding interference with electrical connection wires 106 and stillslidably securely engage to housing 38. Detent 112 provides tactilefeedback to the installer to know when proper sliding engagement isachieved. Following engagement, locking tab 114 may be purposely bent upto engage the rear of rail 104 preventing internal antenna 54 fromdisengaging with housing 38. It is to be recognized and understood thatall of these engaging and locking mechanisms preferably exist on bothsides of implantable medical device 10 in complementary fashion eventhough the drawings illustrate only one side.

An adhesive channel 116 is formed around the perimeter of housing 38.Fill hole 118 communicates through both internal antenna 54 and housing38 to allow an adhesive needle 120 to be inserted. Adhesive needle 120may then be used to fill adhesive channel 116, through fill hole 118,with adhesive providing another layer of sealing for implantable medicaldevice 10.

Once internal antenna 54 is secured to housing 54, electrical connectorwires 106 may be connected using connector block 122 as shown in FIGS.21, 22, 23 and 24. Rigid polysulfone frame 124 provides structuralrigidity to connector block 122. Frame 124 is laid out in linear fashionso that all electrical connections are in a linear row. Wire frame 126is stamped out of a conductive material, preferably a metal. Since rigidframe 124 is laid out linearly, wire frame 126 can be stamped with aplurality of linear connector areas. Wire frame 126 is joined with rigidframe 124 and mated with electrical connector wires 106. Frame cover 128fits over rigid frame 124. Once assembled, a biocompatible thermosetpolymer, such as silicone rubber, can be injected into connector block122 substantially filling any voids in connector block 122 forming athermoset polymer gasket helping to prevent infiltration of body fluidsinto implantable medical device 10. The thermoset polymer (not shown)also provides electrical isolation between the electrical contacts ofwire frame 126.

Connector block 122 has a plurality of openings 130 allowing an externalelectrical connection with implantable medical device 10. Chimneys 132form a void near the external electrical contact openings allowing thethermoset polymer to at least partially fill chimney 132 to further sealand secure an electrical connection opening into implantable medicaldevice 10. Such thermoset polymer also provides a strain relief for thelead used for the external electrical connection. Grommets 134, whichare compatible with thermoset polymer, additionally secure andelectrically isolate the external electrical connection. A set screw 136may be used to mechanically secure the external wire to connector block122. As thermoset polymer substantially fills voids within connectorblock 122, thermoset polymer forms a skirt, when cured, that is usuallythinner than is reasonably possible to be created with rigid frame 124or thermoplastic cover 128. The thinner skirt achieved with thethermoset polymer allows an even stronger and more secure seal againstthe intrusion of body fluids.

In a preferred embodiment, rigid frame is treated before assembly withan adhesion promoter to create a stronger bond between rigid frame 124and thermoset polymer. The surface of polysulfone rigid frame 124 iscleaned with a detergent, preferably Micro 90™ detergent, rinsed firstin D.I. water and then rinsed in IPA. Polysulfone rigid frame 124 isplasma treated by first being placed in a vacuum chamber that is thenevacuated to 0.10 torr vacuum and held for ten (10) minutes. 10 sccm ofHexamethyldisiloxane, 30 sccm of Nitrous oxide and 1 sccm of Argon arepumped into the chamber. Approximately 150 watts of power to ignite theplasma for thirty (30) seconds. Rigid frame 124 is then coated by beingdipped into a twenty percent (20%) solution of RTV medical siliconeadhesive and heptane by weight for approximately two (2) seconds. Rigidframe 124 is then removed from the dip and cured in an oven at 150degrees Centigrade for eight (8) hours.

Thus, embodiments of the connector block for an implantable medicaldevice are disclosed. One skilled in the art will appreciate that thepresent invention can be practiced with embodiments other than thosedisclosed. The disclosed embodiments are presented for purposes ofillustration and not limitation, and the present invention is limitedonly by the claims that follow.

1. A method of overmolding a substrate having a first side and a secondside, comprising the steps of: placing a plurality of support feet onsaid first side of said substrate; placing said substrate in aninjection mold; filling said mold with a molding material with saidmolding material enveloping both said first side and said second side ofsaid substrate; and removing said substrate having been overmolded fromsaid injection mold.
 2. A method of overmolding as in claim 1 whereinmolding material is substantially evenly distributed on said first sideand said second side during said filling step.
 3. A method ofovermolding as in claim 2 wherein said placing a plurality of supportfeet step comprises molding a plurality of support feet on said firstside of said substrate.
 4. A method of overmolding as in claim 1 whereinsaid substrate has a central hub opening.
 5. A method of overmolding asin claim 4 wherein said injection mold has injection openings on oneside of said injection mold and wherein said molding material isinjected into said mold through said injection openings.
 6. A method ofovermolding as in claim 5 wherein said substrate is placed in saidinjection mold with said first side of said substrate facing said oneside of said injection mold.
 7. A method of overmolding as in claim 6wherein said molding material is distributed to said second side of saidsubstrate through said central hub opening.
 8. A method of overmoldingas in claim 1 wherein said feet have a circular cross-section.
 9. Amethod of overmolding as in claim 8 wherein molding material formsaround each of said plurality of feet.
 10. A method of overmolding as inclaim 9 wherein said central hub opening has a circular post aroundwhich said molding material is allowed to form.
 11. An overmoldedsubstrate having a first side and a second side, comprising: a generallyplanar substrate; a plurality of support feet on said first side of saidsubstrate; and a molding material molded around said substrateenveloping said substrate of both said first side and said second sideof said substrate.
 12. An overmolded substrate as in claim 11 whereinsaid support feet are molded in a first molding step and said moldingmaterial is molded around said substrate in a second molding step. 13.An overmolded substrate as in claim 12 wherein molding material issubstantially evenly distributed on said first side and said second sideduring molding;
 14. An overmolded substrate as in claim 11 wherein saidsubstrate is overmolded only from said first side of said substrate. 15.An overmolded substrate as in claim 11 wherein said substrate has acentral hub opening.
 16. An overmolded substrate as in claim 15 whereinsaid molding material is distributed to said second side of saidsubstrate through said central hub opening.
 17. An overmolded substrateas in claim 11 wherein said feet have a circular cross-section.
 18. Anovermolded substrate as in claim 17 wherein molding material formsaround each of said plurality of feet.
 19. An overmolded substrate as inclaim 18 wherein said central hub opening has a circular post aroundwhich said molding material is allowed to form.
 20. An overmoldedsubstrate having a first side and a second side, comprising: a generallyplanar magnetic substrate; a coil positioned on said second side of saidmagnetic substrate; a plurality of support feet on said first side ofsaid magnetic substrate; and a molding material molded around saidsubstrate enveloping said magnetic substrate on both said first side andsaid second side of said magnetic substrate.
 21. An overmolded substrateas in claim 20 wherein said support feet are molded in a first moldingstep and said molding material is molded around said magnetic substratein a second molding step.
 22. An overmolded substrate as in claim 21wherein molding material is substantially evenly distributed on saidfirst side and said second side of said magnetic substrate duringmolding;
 23. An overmolded substrate as in claim 21 wherein said secondside of said molding material is concave.
 24. An overmolded substrate asin claim 20 wherein said magnetic substrate is overmolded only from saidfirst side of said magnetic substrate.
 25. An overmolded substrate as inclaim 20 wherein said magnetic substrate has a central hub opening. 26.An overmolded substrate as in claim 25 wherein said molding material isdistributed to said second side of said magnetic substrate through saidcentral hub opening.
 27. An overmolded substrate as in claim 20 whereinsaid feet have a circular cross-section.
 28. An overmolded substrate asin claim 27 wherein molding material forms around each of said pluralityof feet.
 29. An overmolded substrate as in claim 28 wherein said centralhub opening has a circular post around which said molding material isallowed to form.